textproduct: Rapid City

KEY MESSAGES

- Areas of fog through early Sunday afternoon with dense fog near the MT/WY/SD/ND areas.

- Quiet weather with mild temperatures Sunday.

- Storm system to bring rain, strong northwest winds and light snow over the higher Black Hills on Monday.

UPDATE

Issued at 925 PM MDT Sat Oct 31 2026

Latest nighttime microphysics RGB had stratus/fog slipping southwest into far northeastern WY and slowly sinking south/southeast over northwestern SD as develops. Latest T/Td spreads and circumstantial evidence on highway webcams suggest dense fog will likely continue to develop overnight into Sunday morning over the northwest reaches of the CWA. Have hoisted a Dense Fog Advisory to account.

Latest guidance still shows upper trough/low ejecting into the central Plains Monday bringing robust synoptic lift leading to plenty of precipitation for the CWA. Maybe even some convection Sunday night. Latest ensemble guidance portrays highest QPF totals east of the Black Hills with ECMWF EFI 70-90th percentiles and some shift of tails action. Looks like a pretty good wind event as surface low deepens with upper low. NBM continues to be the strongest with other guidance somewhat weaker (EFI 50-70th percentile wind gusts). Forecast Bufkit soundings similar. Will continue watching event unfold with at least a high end Wind Advisory event expected Monday/Monday night.

DISCUSSION

(This Evening Through Saturday) Issued at 1230 PM MDT Sat Oct 31 2026

Analysis (19z or 1 pm MDT): The longwave flow over the CONUS remains in a trough (west) and ridge (east) pattern with much of the northern Plains sitting between these two features allowing for the SE winds to continue across the region and allowing for our moisture source to be both the monsoon moisture pooled across the Desert SW and portions of the Gulf. This has aided into the formation of the foggy conditions we have seen Friday and again this morning. This trend will continue and we should see patchy fog again on Sunday morning. Latest VIS Satellite image shows most of the fog has dissipated across much of western SD and with skies becoming scattered to clear. With the modest WAA (Warm Air Advection) into the region temperatures have moderated quickly over the past several hours. Current forecast high temperatures today look on track with much of the region seeing temperatures in the low to mid 60s with pockets of lower 70's possible.

Sunday: After what could be some patchy areas of fog to start the day, we can expect another quiet and mild day on Monday with continued breezy southeasterly winds. Temperatures will again warm into the 60s across much of the area. The indicator of the shift in the weather will be the increase in mid to high clouds as we progress through the day on Sunday. We are tracking a large area of low pressure that will be slowly moving through the Intermountain West on Sunday and this will be the system that will bring unsettled weather to the area on Monday and Tuesday.

Models show a strengthening Colorado Low system moving into southern SD Monday morning. Some discrepancies remain on the exact location of low pressure system by overall most models do show a closed low somewhere in central SD Monday morning. This system will be bring rain and wind to western SD. Focusing first on the wind. This low pressure system will continue to deepen as it moves into SD and become sandwiched between two ridges with one remaining over the east coast and on developing across the west coast a belt of strong NW winds develops on the backside of the low and comes directly over much of western SD. Some of models that were showing the highest winds have since backed off a bit and have come into better agreement with most of the ensemble members with current forecast agreement falling in the 45 to 55 mph range for wind gusts on Monday. If this transpires then Wind Advisories will be hoisted. With the feature not developed in this forecast package and location of the low still in question, no wind highlights will be issued this afternoon.

This system will have decent amount of moisture so we are confidence for high end precipitation chances across much of the area on Monday and this should fall in the form of rain for much of the plains and Black Hill Foothills. The best chances for some light snow will be in the highest elevations of the Black Hills. There will be a sharp gradient in precipitation totals which again will depend on the exact track of the low itself, add in the expected downslope wind component and this could eat into some of the totals in these areas. Nonetheless much of area should see some accumulating rains with the highest totals at this time being for locations along and east of the river.

In the wake of the main system on Monday, a fast moving system dives out of ND and pushes through the area quickly on Tuesday. This will bring some cooler temperatures to the region and keep those breezy NW winds in place but these won't be as strong as what we will with the system on Monday. Beyond Tuesday, the rest of the week looks to be quiet with nice fall temperatures expected before we potentially look at another system coming in just in time for next weekend.

AVIATION

(For the 18Z TAFS Through 18Z Monday) Issued At 1040 AM MST Sun Nov 1 2026

Expect continued widespread MVFR/IFR conditions with transient LIFR conditions at times through most of the period. While conditions may begin to slowly and temporarily improve to VFR early this afternoon, rain is expected to move into the region around 19-20z today with MVFR/IFR ceilings overspreading the area through the afternoon and evening hours and last through the remainder of the TAF period. Snow may mix in with the rain for KGCC starting around 02/13z.

Strong northwesterly winds will begin to increase across northeast Wyoming starting around 02/08-09z and across much of western South Dakota around 02/17-18z and last through the TAF period. Isolated gusts may reach 55+kts across the region. KRAP will likely see the stronger wind gusts, however, KGCC will also be impacted.

UNR WATCHES/WARNINGS/ADVISORIES

SD...Dense Fog Advisory until noon MST today for SDZ001-002-012-025- 026-072-078. WY...Dense Fog Advisory until noon MST today for WYZ054-056-057-060.